NEW YORK (CNN) -- An expert on Lincoln photography thinks a photograph found in Gen. Ulysses S. Grant's family-owned album showing President Abraham Lincoln in front of the White House could be one of the last photos taken of the 16th president before he was assassinated in 1865.

"I started to think that it might be the White House," said Grant, a construction business owner from Springfield, Missouri. "Then I started to look at the height difference between the people in the photo."

Thinking that the towering individual commanding the attention of the other people in the image could be Lincoln -- who stood 6-foot-4 and is the nation's tallest president -- Grant called Keya Morgan, a renowned collector and scholar of Lincoln and Gen. Grant photographs, to see whether his suspicions could be verified.

Morgan, who owns the world's largest collection of Lincoln artifacts and original photographs, persuaded Grant to take the small photo out of the album to see whether any clues could be found on the back -- particularly the name of the photographer.

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